The composition and organization of mono- and polynucleosomes in chromatin will be studied in order to contribute to an understanding of the molecular architecture of eukaryotic chromosomes. Two functionally diverse biological systems will be used: bovine thymus tissue and cultured mouse mastocytoma cells (line P815). This project has five major aims: 1. To elucidate micrococcal nuclease mediated precursor-product relationships among mono- and polynucleosomes using two-dimensional electrophoretic techniques (chromatin fingerprinting). 2. To establish the protein compositions of electrophoretically fractionated mononucleosomes by employing: (a) chemical cross-linking reagents, (b) radioisotope procedures, (c) chemical analyses, and (d) two-dimensional gel electrophoresis. 3. To determine the distributions of modified and variant histones with regard to nucleosomal DNA repeat length and the rate of nuclease processing. Methods will include two-dimensional electrophoresis, the use of radioactive isotopes, autoradiography and fluorography. 4. To evaluate whether nucleosome spacing and/or mononucleosome complexity is non-random with respect to specific DNA sequences. Methods of nucleic acid hybridization will be employed. 5. To develop methods to: (a) study the structure and organization of nucleosomes within nascent transcription complexes, and (b) resolve mononucleosomes into species with different combinations of variant histones.